1. Field of the Invention
The present invention relates to a switch mechanism suitable for use in an electrical substation, and to an electrical substation incorporating such a switch mechanism.
2. Summary of the Prior Art
In an electric substation, it is normally necessary to provide a switching mechanism which acts as a circuit breaker for the substation. There are three known types of such switching mechanisms, a first type which operates by spring forces, a second type being a pneumatic system using compressed air, and the third type being a hydraulic system. Spring operated mechanisms are suitable for low voltage circuit breaking, but are not normally suitable for higher voltages. Pneumatic systems have been found to involve excessive maintenance. Hence, particularly in the known puffer-type circuit breaker, requiring a large operating force, hydraulic systems have been developed. An example of such a system is disclosed in JP-A-62-58092.
In existing-hydraulic systems, the hydraulic fluid is mineral oil, and the system is operated at a high pressure of e.g. 300 bars. It should also be noted that it is known to provide an electric substation in which the main circuit conductor is enclosed in an enclosure which is filled with a gas such as sulphur hexafluoride. In existing systems, however, the hydraulic mechanism for activating the movable part of the switching mechanism forming the circuit breaker has been located outside that enclosure. In such circumstances, the hydraulic mechanism may be enclosed in an un-sealed casing, such as disclosed in JP-A-1-220320.
Additionally, in an article entitled "Development of a Perfluorocarbon Liquid Immersed Prototype Large Power Transformer with Compressed SF.sub.6 Gas Installation" by Y. Mukaiyama et al. presented at the IEEE/PES 1990 Summer Meeting, Minneapolis, Minn., 90 SM 465-5 PWRD, an arrangement is proposed wherein a transformer, suitable for use in an electric substation uses perfluorocarbon as a cooling liquid surrounding the core of the transformer, with an outer casing containing sulphur hexafluoride.